Method for detection of rail breaks on occupied blocks to support reduced train spacing

ABSTRACT

A method for detecting broken rail and track occupancies measures both the electrical current and voltage on each end of the block of track. This allows a broken rail to be detected even with a shunting axle (occupancy) in the same detection block. The method also provides broken rail detection capability to support modes of operation in which a following train maintains safe spacing from a leading train without the use of track circuit information for train location, allowing for reduced train spacing. The current and voltage measurements are used to make binary decisions, in order to minimize the sensitivity to variations in track impedance characteristics. When combined with train location information, this method also allows for identifying the location of a rail break.

RELATED APPLICATION

The present application is based on and claims priority to the Applicant's U.S. Provisional Patent Application 62/534,307, entitled “Method for Detection of Rail Breaks on Occupied Blocks to Support Reduced Train Spacing,” filed on Jul. 19, 2017.

GOVERNMENT LICENSE RIGHTS

This invention was made with government support under work sponsored by the Federal Railroad Administration of the U.S. Department of Transportation. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to the field of methods for detecting rail breaks on railroad tracks. More specifically, the present invention discloses a method for detecting rail breaks in occupied blocks of track.

Statement of the Problem

The following definitions apply to the following terms in this disclosure:

“Detection block” means a section of track with defined limits in which broken rails or occupancies can be detected, but that is not limited to a signal block.

“Signal block” means a section of track with defined limits that utilizes conventional wayside or cab signals and may refer to an intermediate, controlled, or absolute permission block.

“Intermediate (automatic) block” means a section of track associated with a single track circuit for automatic block signaling within a controlled block.

“Controlled (absolute) block” means a section of track spanning between control points, the movement into which is controlled by a dispatcher or control operator and may include multiple intermediate blocks.

“Moving block” means a type of train control in which train separation is determined dynamically according to the braking distance of the following train. A moving block is related to a virtual block.

Track circuits are one of the basic components of conventional fixed block railroad signaling systems. Conventional signal systems typically use track circuits to perform two functions: (1) Detect occupancy and broken rails in each block; and (2) Communicate the status of each block to adjacent blocks. Track circuits utilize the steel rails as a path for electrical current flow. The track is separated into electrically isolated sections, or blocks, using insulated joints in the rails to isolate each block. A voltage is placed across the rails at one end of the block and the presence or absence of electrical current is detected at the opposite end of the block. Electrical continuity throughout the length of the block provides information on whether the block is clear of shunting vehicles and broken rails or not. When a train is occupying a block, the wheels and axles of the train shunt the rails together so there is no longer sufficient electrical current at the end of the block to indicate the block is unoccupied. Similarly, a broken rail will result in an open circuit, preventing any current flow through the track circuit. Consequently, track circuits are utilized to detect train occupancy and broken rails.

In conventional signaling systems, signal aspects are determined by the status of the block over which the signal governs movement, as indicated by the track circuit in that block, as well as the status of adjacent blocks. Information about the status of each block is typically transmitted to adjacent blocks through the use of coded track circuits, although there are other methods used in some cases. With coded track circuits, the electrical signal that is transmitted through the rails is coded using different pulse rates to indicate the signal aspect that block is currently displaying. This information is interpreted by the equipment at the adjacent block and used in determining the proper aspect to display for the signal governing movement over that block.

The minimum required length of the track circuit is based on braking distances at track speed and the number of signal aspects that can be displayed. For example, with 4-aspect signaling, the blocks are spaced such that two blocks represent no less than the distance of normal service braking for the worst-case braking train. This creates safe separation between trains as seen in FIG. 1. If a train is detected on a given block, the signals for the preceeding blocks will be ordered by restrictiveness: red (stop), yellow (approach), flashing yellow (advance approach), and green (proceed). Flashing yellow can be used to indicate proceed and prepare to stop at the second signal, or proceed and reduce speed before passing the next signal.

Modern track circuits for freight applications typically use DC coded track circuits. The DC signals sent through the track are pulsed to form codes, providing aspect information that is communicated between the blocks. To allow for bi-directional traffic, DC circuits work in both directions with coordinated pulse timing to avoid interfering with one another. Additional features often include a handshaking protocol to send and receive data within a block, and alternating polarity current to prevent code detection from an adjacent block.

The railroad industry is interested in identifying new technologies that use the rails as the broken rail and track occupancy sensing medium and have potential to support new methods of train control (e.g., communications-based). New train control is intended to improve the capacity of the line with moving block operation and variants thereof. The potential capacity improvement with a moving block (or similar) train control system is limited if conventional fixed blocks are still required to maintain broken rail detection.

Conventional track circuits cannot detect a broken rail that occurs in the same block that a train is occupying since the axles will be shunting the block. The broken rail can then be detected after the train has left that particular block. Also, conventional track circuits do not detect or indicate where within a block a broken rail or occupancy is located. Hence train control systems must protect the entire block when a break or occupancy has been detected. This is the primary limitation in their ability to support moving block operation.

Solution to the Problem

In contrast to the prior art, the present system detects both the current and voltage at the ends of the track circuit. The combination of current and voltage can be used to detect a broken rail even if the block is occupied by a train.

SUMMARY OF THE INVENTION

This invention provides a method for detecting rail breaks in occupied blocks of track by measuring both the current and voltage at the ends of the track circuit. The combination of current and voltage allows detection of a rail break even if the block is occupied.

These and other advantages, features, and objects of the present invention will be more readily understood in view of the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more readily understood in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating track circuits in a 4-aspect block network.

FIG. 2 is a diagram showing conventional track circuit interfaces.

FIG. 3 is a diagram showing next generation track circuit interfaces for PTC and train control.

FIG. 4 is a diagram illustrating examples of a next generation track circuit with transmitting (Tx) current with and without a rail break.

FIG. 5 is a diagram illustrating a next generation track circuit with transmitting current from both ends of a block.

FIG. 6 is a diagram illustrating fixed versus moving block operations.

FIG. 7 is a series of diagrams showing next generation track circuits with broken rail (BR) between trains.

FIG. 8 is a series of diagrams illustrating movement authority when the following train enters an occupied block with no rail break.

FIG. 9 is a series of diagrams corresponding to FIG. 8 illustrating movement authority with a broken rail between trains.

FIG. 10 is a diagram depicting several types of signaled territories.

DETAILED DESCRIPTION OF THE INVENTION

Interfaces and Detection Methods.

Track circuits typically provide binary information for a fixed block. The track circuit can either be clear (i.e., no occupancy and no broken rail) or not clear (i.e., occupancy and/or broken rail). FIG. 2 illustrates a conventional track circuit for a bi-directional track. Each side of the track circuit will transmit (Tx) and receive (Rx) a signal through the track. The conventional track circuit will identify the block as being clear at location A if Rx2 receives from Tx3. Similarly, the track circuit will identify the block as being clear at location B if Rx3 receives from Tx2. This usually includes track signal coordination so only one side of the block is transmitting at a time. The status information for this block is transmitted through the rails to adjacent track circuits with signals Tx1 and Tx4. An adjacent block uses this status information along with what it detects within its own block to determine which signal aspect to display.

With today's PTC (Positive Train Control) and other newer proposed train control systems (especially those that are communications-based), the track circuit information may be transmitted to a server (that may be located in the office) or directly to the locomotive's onboard computer as seen in FIG. 3. In the next generation track circuit, broken rails are similarly detected by monitoring the transmission current. FIG. 4 provides an example of the current loop with the transmitted Tx2 signal. If the signal Tx2 is being transmitted and the current in the loop is substantial (i.e., I≠0), then the track circuit is clear of broken rails within that current loop. If the signal Tx2 is being transmitted and the current loop is near zero (i.e., I=0), then there is a broken rail. There is likely a negligible amount of current flowing through the ballast. Consequently, this method allows for the detection of broken rails, even with a shunting axle on the block, but does not distinguish if the track circuit is occupied or unoccupied if no further information is available.

Monitoring of the transmission current can be performed on each side of the track circuit. FIG. 5 provides an example of the current loops from both the transmitted Tx2 and Tx3 signals. Further considerations regarding the monitoring of transmission current include: (1) A broken rail can be detected anywhere between a shunting axle and the respective end of the block; (2) Since the Tx2 and Tx3 signals are being time-coordinated, so will the monitoring of the transmission current through the track as detected at each end of the block; (3) Binary information is obtained from monitoring the transmission current (i.e., broken rail or not); and (4) Even though broken rail information is provided both in front of and behind a train, the relevant information for that train will be ahead of it. Technology is available in which a track database plus an onboard positioning system can be used to process the location and direction of a vehicle.

In the present methodology, additional information is obtained by also monitoring of voltage by the next generation track circuit. If the voltage detected at A and/or B drops to approximately zero, but the current in the block is substantial, then an occupancy can be determined to be present in the block. This produces additional binary information from each end of the block. Table 1 presents the various combinations of information provided by voltage and current for each end of the block. The next generation track circuit can also be used to detect an open or shunt caused by a device (e.g., turnout or track obstruction detector) interfaced with the track circuit.

TABLE 1 Possible combinations of voltage and current for ends A and B of the block |V_(Rx)| |I_(Tx)| (A) |V_(Rx)| (A) |I_(Tx)| (B) (B) Indication >0 >0 >0 >0 Clear 0 0 0 0 Broken Rail - No Occupancy Or Occupied - Broken Rail Between A and Occupancy; and Broken Rail Between B and Occupancy Note: The ambiguity is resolved when the locomotive onboard system knows it is occupying the block. >0 0 >0 0 Occupied - No Broken Rail 0 0 >0 0 Occupied - Broken Rail Between A and Occupancy >0 0 0 0 Occupied - Broken Rail Between B and Occupancy Note: In the table, 0 means near zero or within a defined threshold.

Moving Blocks.

In this disclosure, modern train control is understood to be a moving block or similar (e.g., virtual block) operation. The advantage of moving blocks compared to fixed block operation is seen in FIG. 6. Fixed blocks with 4-aspect signaling are spaced such that the length of two blocks represent no less than the distance of normal service braking for the worst-case braking train. A following train that is slightly less than three blocks from the rear of the train ahead and operating at or near track speed will have to reduce speed. Therefore, the minimum steady-state train separation that can be maintained between two trains operating at track speed is three blocks, using 4-aspect signaling. Moving block operation will theoretically allow the following train to be at its braking distance, with some additional warning distance and margin, from the leading train.

Detection Blocks.

The concept for next generation track circuits is to perform as detection blocks that provide broken rail identification and roll-out protection against unexpected or unmonitored occupancies. The next generation control system can use the binary track circuit status information for these functions but does not require it for train location determination and separation, all of which are available functions with conventional track circuits.

Next generation track circuit technology will improve the spatial and temporal resolution of rail breaks compared with conventional track circuit technology. The proposed next generation track circuit method utilizes both electrical voltage and current on both ends of the detection block as described above. This improves the spatial resolution as a broken rail can be detected between a shunting axle and one end of the block. The spatial resolution of rail break location can be improved even more significantly if the train control system uses rear-of-train location reported by a leading train in conjunction with the next generation track circuit information described here. Furthermore, temporal resolution is improved in the sense that a broken rail can be detected while there is a shunting axle in the block. Conventional technology can only detect a broken rail once the signal block is unoccupied.

In conventional fixed block signaling systems, the minimum length of the signal block is determined by the braking distance of the trains operating over the territory at the maximum allowable speed. This provides safe separation of trains. In a modern train control system with next generation track circuits, safe separation of trains is provided by a moving block train control method. Furthermore, the track circuits communicate status to trains in the area through a wireless communications system or to a server via any of various communications media, as opposed to only communicating status via signal aspect to trains approaching the block. In this concept, longer detection blocks may be practical but can reduce the potential capacity gained through the moving block train control system. Therefore, it is the maximum detection block length that needs to be specified, in order to optimize the capacity of the operation with a modern train control system.

In other words, while in conventional fixed block signal systems, the minimum length of the signal block is determined to provide safe train separation for a specified number of available signal aspects, in this system, the maximum length of the detection block is determined to provide the desired balance between track circuit cost and line capacity. For the next generation track circuit, the length of the track circuit is still driven by the braking distance of the train, including the desired warning distance: (1) If the braking distance plus warning distance is less than the detection block length, train separation is dictated by the detection blocks; or (2) If the braking distance plus warning distance is greater than the detection block length, train separation is dictated by the moving block train control system. Therefore, with this system, an analysis of the utilization of each specific line where it is to be implemented and the typical braking distance plus warning distance of the trains operating on the line should be conducted to optimize the length of the detection blocks on the line.

Broken Rails Between Trains.

The next generation track circuit detects broken rails between trains, albeit before they simultaneously occupy the same block. The proposed concept is for broken rails to be detected by the received voltage signal as well as monitoring the current in the loop, as described above. Monitoring the current in the loop allows a broken rail to be detected, even if an axle is shunting in the same detection block, as long as the train is not spanning across the broken rail. FIG. 7 provides illustrations of a broken rail and how it would be detected between trains using this concept.

Once the broken rail is detected, the information will be transmitted to the office (or other off-board system) and/or locomotive. Enforcement braking will occur in time to stop the train before reaching the rail break. If a train is following another train as closely as the moving block control system will allow (i.e., by the warning distance), and the broken rail occurs directly beneath the leading train, the break will be detected as soon as the leading train is no longer over the break, leaving sufficient time for the following train to receive the broken rail notification and stop short of the broken rail as long as the following train has not yet entered the block.

Movement Authorities.

The context for the next generation track circuit is that train separation is controlled by modern methods of train control (e.g., moving block). The train control system will separate the following train from the rear of the leading train by the following train's braking distance plus warning distance and margin. Modern train control systems use movement authorities and/or stop targets to ensure train separation. In order to apply the proposed next generation track circuit the following rules should be considered.

A movement authority rule could be designed into the system to account for the case when a following train enters an occupied detection block, thereby masking the broken rail protection between trains. See FIG. 8, which illustrates movement authority when the following train enters an occupied block with no rail break. This case is possible if the braking distance for the following train is less than the detection block length. To restore broken rail detection, a stop target is held corresponding to the last reported end-of-train location of the leading train at the time when the following train enters the occupied block, when no rail break has been detected in the occupied block up to that time. Entering an occupied block can be determined by a database with detection block boundary locations and the known head of train location.

The stop target would be replaced with a new stop target behind the latest reported leading train location once the leading train clears the block and the track circuit determines there is no rail break in the block in advance of the following train. Clearing an occupied block can be determined by a database with detection block boundary locations and the known rear of train location

The proposed movement authority rule would be designed into the system to protect the following train in the case of broken rails between trains. See FIG. 9, which illustrates movement authority with a broken rail between trains. The office/server would need to process the following pieces of information: (A) last reported end-of-train location of the leading train at the time when (B) the transmission current behind the leading train changes to I=0 amps. Once this state change occurs, the corresponding location becomes the limit of the movement authority for the following train. Note that additional broken rails could occur underneath the leading train. The first detected broken rail will remain as the limit of the movement authority since that is the only possible instance when the transmission current Tx changed to I=0 amps.

Deployment.

Next generation track circuits may also need to support current methods of operation in different types of signaled territory, as seen in FIG. 10. With Centralized Traffic Control (CTC), the dispatcher manages traffic remotely between Control Points (CPs). The intermediate blocks between CPs are automatically controlled with track circuits and provide for train separation. Ensuring train separation between CPs may eventually migrate to modern train control. Therefore, next generation track circuits should provide the two functions of conventional signal systems: (1) Detect occupancy and broken rails in each block; and (2) Communicate the status of each block to adjacent blocks. Migration to modern train control may eventually eliminate the need for the second function. However, next generation track circuits could keep the function of communicating status to adjacent blocks as a fallback function. PTC territory and high capacity lines are examples of territories that may benefit from modern train control and next generation track circuits. High capacity lines can take advantage of modern train control to increase volume and reduce delay

The above disclosure sets forth a number of embodiments of the present invention described in detail with respect to the accompanying drawings. Those skilled in this art will appreciate that various changes, modifications, other structural arrangements, and other embodiments could be practiced under the teachings of the present invention without departing from the scope of this invention as set forth in the following claims. 

We claim:
 1. A method for detecting rail breaks in a block of track having first and second ends, said method comprising applying a voltage across the tracks at the first end and detecting the resulting voltage and current at the second end; applying a voltage across the tracks at the second end and detecting the resulting voltage and current at the first end; and determining the existence of broken rail from the combination of voltages and currents detected at the first and second ends.
 2. The method of claim 1 wherein the block of track is determined to be unoccupied by a vehicle and to have no broken rail if the magnitudes of all of the detected voltages and currents exceed predetermined threshold values.
 3. The method of claim 1 wherein the block of track is determined to have a broken rail if the block of track is unoccupied by a vehicle and the magnitudes of all of the detected voltages and currents do not exceed predetermined threshold values.
 4. The method of claim 1 wherein, if the block of track is occupied by a vehicle, the block of track is determined to have a broken rail between the first end and the vehicle, and a broken rail between the second end and the vehicle, if the magnitudes of all of the detected voltages and currents do not exceed predetermined threshold values.
 5. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle and to have no broken rail if the magnitudes of the detected voltages at both ends are do not exceed predetermined threshold values, and the magnitudes of the detected currents at both ends exceed predetermined threshold values.
 6. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle and to have a broken rail between the first end and the vehicle if the magnitude of the current detected at the second end exceeds a predetermined threshold value and the magnitudes of the other detected voltages and currents do not exceed predetermined threshold values.
 7. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle and to have a broken rail between the second end and the vehicle if the magnitude of the current detected at the first end exceeds a predetermined threshold value and the magnitudes of the other detected voltages and currents do not exceed predetermined threshold values.
 8. The method of claim 1 wherein the block of track is determined to have a broken rail if the magnitude of the current detected at either the first end or the second end does not exceed a predetermined threshold value.
 9. The method of claim 1 wherein the block of track is determined to be occupied by a vehicle if the magnitude of the detected voltage at either the first end or the second end does not exceed a predetermined threshold value.
 10. The method of claim 1 further comprising limiting the movement authority of a following vehicle behind a leading vehicle on the block of track by determining the location of the leading train on the block of track when the magnitude of the current detected behind the leading vehicle falls below a predetermined threshold value.
 11. The method of claim 1 further comprising limiting the movement authority of a following vehicle behind a leading vehicle on the block of track by determining the location of the leading train on the block of track when the following train enters the block.
 12. The method of claim 1 wherein the block of track has a length determined by the braking distance plus a warning distance for trains operating on the track.
 13. The method of claim 1 further comprising determining the location of the rail break in a block of track having a vehicle moving along the block of track by determining the location of the vehicle when the magnitude of the current detected behind the vehicle falls below a predetermined threshold value. 